Guiding Properties of a Photonic Quasi-Crystal Fiber Based on the Thue-Morse Sequence

We present a novel microstructured optical fiber
having a quasi-periodic distribution of air holes based on the
Thue-Morse sequence. The transverse section of these fibers is
basically a two-dimensional photonic quasi-crystal that can also
provide complete photonic bandgaps without being a perfect
periodic structure. Like in the conventional photonic crystal
fibers, if the quasi-periodicity is broken by decreasing the size of
some air holes or by introducing an extra air hole, the modified
holes become defects that localize and guide light along the fiber.
The guidance is attributed to the inhibition of transverse radia-
tion produced by the photonic quasi-crystal cladding. Dispersion
curves of guided modes for different structural parameters are
calculated, along with the transverse intensity distribution of
the fundamental mode. In particular, several specially designed
Thue-Morse quasi-crystal fibers with nearly zero ultraflattened group-velocity dispersion are presented.